little confused here, what is the application here? Why are you storing water in the tanks, or are they tanks for a demand system. Put the pictures up.

On the surface it sounds like your canal filters are fouled or the debris through the system has fubared the impellers, or debris is keeping one from rotating or the wiring is phuked or maybe it's burned out all together. At least Pull the line & clean the filter or go swimming... dismantle the volute and clear the crap. Sounds like a lot od $hit going on for a small system. Why two pumps at all?

Sounds like it could be clogged foot valve(s).
I'd also check the threaded pvc connections at the pump intakes. If the pumps got hot from lack of water then the pvc fittings may be damaged, allowing air to be sucked in causing loss of prime.

You should alwayds run a galvanized steel fitting on the pressure side as a heat sink before attaching PVC... and then the PVC should be sched 80.

check the inlets for possible cracks caused by vibration and heat. air could be coming in through hairline cracks between the threads of the male adapter, or nipple, or whatever is making the inlet connection.

check for clogs as well. i would redo all inlet connections to eliminate air intake possibilities.

also, how many vertical feet is the pump "sucking" water up? there is a limit to that... something like 26-28 vertical ft lift or something?